23 February 2015 | 11:32
By Jan Gorgol

Cont.

Humidity Effects on Structure in Regenerative Tissue Engineering

Tissue engineering is growing as an area of research which aims to regenerate damaged tissues such as perforated eardrum membranes.

This is achieved through the use of biomaterials which provide cells with the necessary biological triggers to induce cell growth. The process involves collecting healthy cells from the patient’s body, expanding the cells, and culturing them on a porous support structure known as a scaffold.

Ideally, the cells adhere to the scaffold, reproduce, and deposit extra-cellular matrix at the same rate at which the scaffold degrades, resulting in healthy, functional tissue.

Making such a scaffold which meets these criteria poses a big challenge, and electrospinning has emerged as a simple cost effective production method. Electrospinning uses a high voltage electric field to draw a polymer solution flowing out of a capillary into solid nanofibers.

Dr. Wankei’s group at the University of Western Ontario excells at looking at Bio Nanomaterials related to medical device area and has looked at the effects of humidity on the morphology, and the core-shell structure of such electrospun nanofibers.[2]

Initially core-shell nanofibers composed of a poly(caprolactone) and poly(ethylene glycol) core were created using electrospinning at relative humidity values of 20, 25, 30, and 40% within a glove box with humidity control.

The morphology of the fibres was studied using SEM, TEM and laser scanning confocal microscopy. Relative humidity (RH) can interfere with the electrospinning process, making it impossible under certain conditions. It was found that humidity altered the rate at which the fibres dry and that there is an optimal humidity for the coaxial electrospinning of core-shell fibres.

At very low humidity levels the solvent tends to dry quickly so that the jet can dry up, causing the needle to clog and preventing electrospinning. Alternatively at very high humidity conditions the polymer solution is unable to form coherent fibers and electrospraying occurs instead Ambient RH has an influence on the electrospinning process with the general trend that an increase in RH causes a decrease in fiber diameter. In the case of a polymer solution which utilizes water as the solvent, the mechanism for this effect is as the RH decreases, the amount of water vapour in the environment also decreases. This leads to the evaporation of water from the polymer solution resulting in an increased evaporation rate and quicker solidification of the fiber.

The dominating effect depends wholly on the hydrophobic or hydrophilic properties of the polymer solution being utilized. It was found that humidity affects the core-shell structure by altering how quickly the fibers dry as they travel between the needle and collector electrode. The fiber diameter increased with decreasing humidity, an effect seen with solid fibers. At high RH values, the fibers take a longer time to dry resulting in greater fiber fusion during deposition. Ultimately, the knowledge gained helps engineer more efficient tissue regeneration systems.

Mositure Effects on Carbon Fiber Polymer-Matrix Composites

Moisture is known to affect negatively numerous properties of polymers and their composites. A lot of researchers have looked at the effect of moisture on the mechanical behaviour of polymer-matrix composites, and how to address the fact that the mechanical behaviour is strongly related to the effectiveness for structural applications. In the case of carbon fiber epoxy-matrix composites, the properties which are dominated by the matrix or the fiber-matrix interface are degraded by moisture absorption, whereas the properties that are dominated by the fibers themselves are basically not affected. In particular, the interfacial strength, interlaminar tensile strength and strain-energy release rate are all degraded by moisture. This degradation is attributed to the weakening of the fiber-matrix bond, the matrix softening due to water swelling and the related loss of matrix shear strength. On the other hand, the matrix can be plasticized by water increasing the fracture (delamination) toughness causing moisture to have little effect on the fracture properties.

The above are just a few examples on the micro and nano scale showing how humidity effects on fibers mechanical, structural and morphological properties can be valuably studied in practical industrial and medical applications. To help meet Scientists and Technician’s many needs in these areas Surface Measurement Systems have developed the GenRH humidity generation series including the environmental microscopy cell GenRH-Mcell [3] to enable precise critical humidity studies in situ.

Please feel welcome to contact Mr Jan Gorgol if you have any humidity generation needs in such diverse areas.

References
[1] Releasing tool-adhered natural fibrous micro-scale objects with vacuum system
Yuli Lai ; Cervinka, T. ; Kallio, P. IEEE/ASME International Conference on Advanced Intelligent Mechatronics (AIM), 2014  Besacon, France 8-11 July 2014 Page(s):378 – 383
[2]  “Humidity Effect on the Structure of Electrospun Core-Shell PCL-PEG Fibers for Tissue Regeneration Applications” Golin, Adam P., (2014). University of Western Ontario – Electronic Thesis and Dissertation Repository. Paper 1999
[3] Surface Measurement Systems Application Note 501 – Environmental Microscopy using the GenRH-A Humidity Generator and Mcell Accessory.

About the author:

Jan Gorgol studied Physics at Bristol University followed by a Masters at Brunel University while working with XPS & SEM at the Experimental Techniques Centre. After working extensively in surface science instrumentation globally he now is Product Manager for the GenRH series of humidity generation products at Surface Measurement Systems Ltd.

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